The present invention relates to printing plate imaging and particularly to the feeding of an external drum imager with plates directly from a web of printing plate stock.
External drum printing plate imagers have a drum with clamps extending axially along the surface of the drum with one clamp for the leading end of a printing plate and another clamp appropriately spaced for the trailing end of the plate. The printing plate is imaged by clamping it onto the drum and then rotating the drum in the imaging apparatus with the imaging radiation scanning the plate.
In the conventional operation of an external drum imager, there is a stack of printing plates which have been pre-cut to the appropriate size usually with interleaving sheets of paper between adjacent plates to protect the imageable coating on the front faces of the plates from contact with the back faces of the adjacent plates. With automatic operation, each plate is picked up from the stack, usually by vacuum fingers, and loaded into the clamps on the drum. Provision must also be made for removing and disposing of the interleaving paper. This loading process is then repeated for each plate to be imaged.
The object of the present invention is to simplify the loading of printing plates onto an external drum imager. The invention involves the feeding of a web of printing plate stock to the drum and then cutting the web to form an individual plate of the appropriate length. The drum is then rotated so that the cut plate with the leading end clamped to the drum is wrapped around the drum and the trailing end clamped. The plate is then ready for imaging and unloading from the drum in a conventional manner.